You do realise that we have been altering things for centuries. Cross-breeding plants to create new varities of say fruits? Isn't that a form of Genetic alteration?
A crop could in theory be altered so it needs less water to grow, or be made resistant to a particular blight.
Which could in theory mean higher crop yields, less crop loss due to disease etc..
That isn't to say all ideas for GM are good, it just that some might have uses.
And remember humans are part of nature as well, and nature has given us our intelligence over the course of our evolution.
As for labelling that is of course a different issue, and yes perhaps they should be labelled as such. but just to be safe like a great many foods carry a warning today, that it may contain nuts. Shouldn't all food carry the warning it may contain GM food.
After all you never can be 100% certain somewhere along the production line it has never come into contact with it.